The company's shares rose 9.2 percent.

HeartWare's left ventricular assist device, or LVAD, is designed to be implanted in the chest near the heart and used inside or outside the hospital.

The device will compete with Thoratec Corp's HeartMate II, which has been sold in the United States since 2008 and had been the only heat pump available to heart failure patients awaiting a transplant.

Some investors have bet that HeartWare's device will eclipse the HeartMate II because it is smaller and takes less time to implant. However, concerns about pump-associated thrombosis, or the formation of blood clots, as well as stroke, could hurt the HeartWare device's market share.

HeartWare's shares have slumped about 15 percent in the past six weeks as investors grew nervous about whether the product would be approved.

The FDA said the life-saving benefits of the device in the intended population of patients with end-stage heart failure outweighed risks observed during the clinical trial, such as infection and stroke.

J.P. Morgan analyst Michael Weinstein said the approval could propel revenue growth of at least 30 percent a year for HeartWare, with half of the expected volume generated by market share taken from Thoratec.

He expects HeartWare's shares to recoup much of their recent losses with the U.S. approval. The device is already sold in Europe.

The device was approved based on data from a study of 137 patients with advanced heart failure who received the HeartWare LVAD. The data was compared with outcomes from patients followed by a medical database who used other mechanically assisted circulatory support systems.

It was the first time the FDA has approved an LVAD using information from a database as a comparison, the agency said.

Heart failure is considered end stage when the underlying condition no longer responds to medical therapy or other treatment options. LVADs can be used as a bridge therapy for patients until a donor heart becomes available.

An estimated 50,000 people around the world are candidates for a heart transplant, but only about 5,000 get one each year.

Shares of HeartWare, based in Framingham, Massachusetts, climbed $7.53, or 9.18 percent, to end at $89.54 on Tuesday on the Nasdaq. Shares of Thoratec, based in Pleasanton, California, fell 39 cents, or 1.1 percent, to close at $35.

(Reporting By Susan Kelly in Chicago; Editing by Gerald E. McCormick, G Crosse, Carol Bishopric and Steve Orlofsky)

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